AlGaN/GaN-based HEMT on SiC substrate for microwave characteristics using different passivation layers

Abstract

In this paper, a new gate-recessed AlGaN/GaN-based high electron mobility transistor (HEMT) on SiC substrate is proposed and its DC as well as microwave characteristics are discussed for Si3N4 and SiO2 passivation layers using technology computer aided design (TCAD). The two-dimensional electron gas (2DEG) transport properties are discussed by solving Schrodinger and Poisson equations self-consistently resulting in various subbands having electron eigenvalues. From DC characteristics, the saturation drain currents are measured to be 600 mA/mm and 550 mA/mm for Si3N4 and SiO2 passivation layers respectively. Apart from DC, small-signal AC analysis has been done using two-port network for various microwave parameters. The extrinsic transconductance parameters are measured to be 131.7 mS/mm at a gate voltage of Vgs = −0.35 V and 114.6 mS/mm at a gate voltage of Vgs = −0.4 V for Si3N4 and SiO2 passivation layers respectively. The current gain cut-off frequencies (ft) are measured to be 27.1 GHz and 23.97 GHz in unit-gain-point method at a gate voltage of −0.4 V for Si3N4 and SiO2 passivation layers respectively. Similarly, the power gain cut-off frequencies (fmax) are measured to be 41 GHz and 38.5 GHz in unit-gain-point method at a gate voltage of −0.1 V for Si3N4 and SiO2 passivation layers respectively. Furthermore, the maximum frequency of oscillation or unit power gain (MUG = 1) cut-off frequencies for Si3N4 and SiO2 passivation layers are measured to be 32 GHz and 28 GHz respectively from MUG curves and the unit current gain, ∣ h21 ∣ = 1 cut-off frequencies are measured to be 140 GHz and 75 GHz for Si3N4 and SiO2 passivation layers respectively from the abs ∣ h21 ∣ curves. HEMT with Si3N4 passivation layer gives better results than HEMT with SiO2 passivation layer.